Synchronous replication for storage

ABSTRACT

One or more techniques and/or computing devices are provided for implementing synchronous replication. For example, a synchronous replication relationship may be established between a first storage controller hosting local storage and a second storage controller hosting remote storage (e.g., replication may be specified at a file, logical unit number (LUN), or any other level of granularity). Data operations and offloaded operations may be implemented in parallel upon the local storage and the remote storage. Error handling operations may be implemented upon the local storage and implement in parallel as a best effort on the remote storage, and a reconciliation may be performed to identify any data divergence from the best effort parallel implementation. Storage area network (SAN) operations may be implemented upon the local storage, and upon local completion may be remotely implemented upon the remote storage.

RELATED APPLICATION

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 15/850,754, filed on Dec. 21, 2017 and titled“SYNCHRONOUS REPLICATION FOR STORAGE AREA NETWORK PROTOCOL STORAGE,”which claims priority to and is a continuation of U.S. Pat. No.9,917,896, filed on Nov. 27, 2015 and titled “SYNCHRONOUS REPLICATIONFOR STORAGE AREA NETWORK PROTOCOL STORAGE,” which is incorporated hereinby reference.

BACKGROUND

A storage environment may provide clients with access to data usingstorage area network (SAN) protocols, such as through Small ComputerSystem Interface (SCSI), internet SCSI (iSCIS), Fiber Channel Protocol(FCP), etc. In an example, the storage environment may comprise one ormore storage controllers configured to provide clients with access todata within storage devices owned by such storage controllers. Forexample, a first storage controller may provide clients with access todata within a first storage device. A second storage controller mayprovide clients with access to data within a second storage device.

A synchronous replication relationship may be established between thefirst storage controller and the second storage controller, which mayimprove data loss protection and mitigate client interruptions ofservice in the event a storage controller and/or storage device fails orbecomes unavailable. For example, data may be replicated from the firststorage device to a secondary storage device (e.g., replicated to astorage device accessible to the second storage controller but initiallyowned by the first storage controller) so that the second storagecontroller may provide clients with failover access to replicated datawithin the secondary storage device in the event the first storagecontroller fails. In an example of synchronous replication, a writerequest, targeting the first storage device, may be split into a localwrite request that is to be performed upon the first storage device anda remote write request that it to be performed upon the secondarystorage device (e.g., the local write request may be performed firstupon the first storage device, and upon completion of the local writerequest, the remote write request may be performed upon the secondstorage device). Once both the local write request and the remote writerequest are complete, a write request complete notification may beprovided back to a client that issued the write request. In an example,the local write request and the remote write request may be performed inparallel. Unfortunately, synchronous replication may be implementedwithin a file system, and thus changes to the file system may render thesynchronous replication inoperable. Additionally, synchronousreplication may be merely available at a coarse level of granularity,such as a volume level or storage controller level, and thus resourcesthat may otherwise be used for storage operations and client data accessmay be undesirably consumed by overhead associated with coarse grainsynchronous replication (e.g., a volume may comprise some files that aclient wants replicated and other files for which the client is notinterested in replication, but volume level replication may replicateall files of the volume).

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in accordance with one or more of the provisions set forthherein.

FIG. 2 is a component block diagram illustrating an example data storagesystem in accordance with one or more of the provisions set forthherein.

FIG. 3 is a flow chart illustrating an exemplary method of synchronousreplication.

FIG. 4A is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a data operation is received.

FIG. 4B is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a data operation is locallyimplemented and a replication data operation is remotely implemented inparallel.

FIG. 4C is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a data operation completenotification is provided to a host.

FIG. 5A is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where an offloaded operation isreceived.

FIG. 5B is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where an offloaded operation islocally implemented and a replication offloaded operation is remotelyimplemented in parallel.

FIG. 5C is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where an offloaded operationcomplete notification is provided to a host.

FIG. 6A is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a storage area networkoperation is received.

FIG. 6B is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a storage area networkoperation is locally implemented.

FIG. 6C is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where local implementation of astorage area network operation is completed.

FIG. 6D is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a replication storage areanetwork operation is remotely implemented.

FIG. 6E is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where remote implementation of areplication storage area network operation is completed.

FIG. 6F is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a storage area networkoperation complete notification is provided to a host.

FIG. 7A is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where an error handling operation isreceived.

FIG. 7B is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where an error handling operation islocally implemented and a replication error handling operation isremotely implemented as a best effort and in parallel with the errorhandling operation.

FIG. 7C is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where an error handling operationsuccess notification is provided to a host.

FIG. 7D is a component block diagram illustrating an exemplary computingdevice for synchronous replication, where a reconciliation between localstorage and remote storage is performed.

FIG. 8 is an example of a computer readable medium in accordance withone or more of the provisions set forth herein.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

One or more techniques and/or computing devices for synchronousreplication are provided. Synchronous replication may be provided forstorage accessible through a storage area network (SAN) protocol, suchas using SCSI, iSCSI, FCP, etc. The synchronous replication may beprovided above a file system such that operations (e.g., inband SCSI opssuch as write, unmap, copy offload, etc.; out-of-band metadata ops suchas logical unit number (LUN) modify, resize, etc.) may be interceptedbefore reaching the file system, and thus synchronous replication may beunaffected by changes to the file system (e.g., a file system upgrade, achange from a first file system to a second file system, etc.) and/ormay be file system agnostic (e.g., synchronous replication functionalitymay be compatible with various types of file systems).

The synchronous replication may be provided at a relatively finer levelof granularity, such as for a single file, LUN, or a consistency groupof files or LUNs, which may reduce processing resources and networkbandwidth otherwise wasted on relatively coarser grain synchronizationthat synchronizes more files, LUNs, or data than desired (e.g., a volumelevel synchronization may replicate all files of a volume regardless ofwhether the volume comprises some files for which replication is notneeded). It may be appreciated that in one example where synchronousreplication is implement for the SAN protocol, replication may beprovided at a LUN granularity. Synchronous replication may implementdata operations (e.g., a write operation) in parallel, implementoffloaded operations (e.g., a copy offload operation) in parallel withone another and serialized with inflight file operations, implementerror handling operations (e.g., an abort task, a task set, a LUN reset,a target reset, etc.) on local storage and as a best effort on remotestorage, and implement SAN control operations (e.g., a set LUN size, aspace reservation, or other changes to storage object metadata)sequentially and serially for the same target storage object (e.g.,serial implementation of 2 SAN control operations for the same LUN).

To provide context for synchronous replication, FIG. 1 illustrates anembodiment of a clustered network environment 100 or a network storageenvironment. It may be appreciated, however, that the techniques, etc.described herein may be implemented within the clustered networkenvironment 100, a non-cluster network environment, and/or a variety ofother computing environments, such as a desktop computing environment.That is, the instant disclosure, including the scope of the appendedclaims, is not meant to be limited to the examples provided herein. Itwill be appreciated that where the same or similar components, elements,features, items, modules, etc. are illustrated in later figures but werepreviously discussed with regard to prior figures, that a similar (e.g.,redundant) discussion of the same may be omitted when describing thesubsequent figures (e.g., for purposes of simplicity and ease ofunderstanding).

FIG. 1 is a block diagram illustrating the clustered network environment100 that may implement at least some embodiments of the techniquesand/or systems described herein. The clustered network environment 100comprises data storage systems 102 and 104 that are coupled over acluster fabric 106, such as a computing network embodied as a privateInfiniband, Fibre Channel (FC), a logical connection, or Ethernetnetwork facilitating communication between the data storage systems 102and 104 (and one or more modules, component, etc. therein, such as,nodes 116 and 118, for example). It will be appreciated that while twodata storage systems 102 and 104 and two nodes 116 and 118 areillustrated in FIG. 1, that any suitable number of such components iscontemplated. In an example, nodes 116, 118 comprise storage controllers(e.g., node 116 may comprise a primary or first storage controller andnode 118 may comprise a secondary or second storage controller) thatprovide client devices, such as host devices 108, 110, with access todata stored within data storage devices 128, 130. Similarly, unlessspecifically provided otherwise herein, the same is true for othermodules, elements, features, items, etc. referenced herein and/orillustrated in the accompanying drawings. That is, a particular numberof components, modules, elements, features, items, etc. disclosed hereinis not meant to be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, in one embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while in another embodiment a clustered networkcan include data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more host devices 108, 110 which maycomprise, for example, client devices, personal computers (PCs),computing devices used for storage (e.g., storage servers), and othercomputers or peripheral devices (e.g., printers), are coupled to therespective data storage systems 102, 104 by storage network connections112, 114. Network connection may comprise a local area network (LAN) orwide area network (WAN), for example, that utilizes Network AttachedStorage (NAS) protocols, such as a Common Internet File System (CIFS)protocol or a Network File System (NFS) protocol, or Storage AreaNetwork (SAN) protocols, such as internet Small Computer SystemInterface (iSCSI) or Fibre Channel (FC) protocol, to exchange datapackets. Illustratively, the host devices 108, 110 may begeneral-purpose computers running applications, and may interact withthe data storage systems 102, 104 using a client/server model forexchange of information. That is, the host device may request data fromthe data storage system (e.g., data on a storage device managed by anetwork storage control configured to process I/O commands issued by thehost device for the storage device), and the data storage system mayreturn results of the request to the host device via one or more storagenetwork connections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, cloud storage (e.g., a storage endpoint may bestored within a data cloud), etc., for example. Such a node in theclustered network environment 100 can be a device attached to thenetwork as a connection point, redistribution point or communicationendpoint, for example. A node may be capable of sending, receiving,and/or forwarding information over a network communications channel, andcould comprise any device that meets any or all of these criteria. Oneexample of a node may be a data storage and management server attachedto a network, where the server can comprise a general purpose computeror a computing device particularly configured to operate as a server ina data storage and management system.

In an example, a first cluster of nodes such as the nodes 116, 118(e.g., a first set of storage controllers configured to provide accessto a first storage aggregate comprising a first logical grouping of oneor more storage devices) may be located on a first storage site. Asecond cluster of nodes, not illustrated, may be located at a secondstorage site (e.g., a second set of storage controllers configured toprovide access to a second storage aggregate comprising a second logicalgrouping of one or more storage devices). The first cluster of nodes andthe second cluster of nodes may be configured according to a disasterrecovery configuration where a surviving cluster of nodes providesswitchover access to storage devices of a disaster cluster of nodes inthe event a disaster occurs at a disaster storage site comprising thedisaster cluster of nodes (e.g., the first cluster of nodes providesclient devices with switchover data access to storage devices of thesecond storage aggregate in the event a disaster occurs at the secondstorage site).

As illustrated in the clustered network environment 100, nodes 116, 118can comprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise network modules 120, 122 and data modules 124, 126. Networkmodules 120, 122 can be configured to allow the nodes 116, 118 (e.g.,network storage controllers) to connect with host devices 108, 110 overthe storage network connections 112, 114, for example, allowing the hostdevices 108, 110 to access data stored in the distributed storagesystem. Further, the network modules 120, 122 can provide connectionswith one or more other components through the cluster fabric 106. Forexample, in FIG. 1, the network module 120 of node 116 can access asecond data storage device 130 by sending a request through the datamodule 126 of a second node 118.

Data modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, data modules 124, 126 communicate with the data storage devices128, 130 according to a storage area network (SAN) protocol, such asSmall Computer System Interface (SCSI) or Fiber Channel Protocol (FCP),for example. Thus, as seen from an operating system on nodes 116, 118,the data storage devices 128, 130 can appear as locally attached to theoperating system. In this manner, different nodes 116, 118, etc. mayaccess data blocks through the operating system, rather than expresslyrequesting abstract files.

It should be appreciated that, while the clustered network environment100 illustrates an equal number of network and data modules, otherembodiments may comprise a differing number of these modules. Forexample, there may be a plurality of network and data modulesinterconnected in a cluster that does not have a one-to-onecorrespondence between the network and data modules. That is, differentnodes can have a different number of network and data modules, and thesame node can have a different number of network modules than datamodules.

Further, a host device 108, 110 can be networked with the nodes 116, 118in the cluster, over the storage networking connections 112, 114. As anexample, respective host devices 108, 110 that are networked to acluster may request services (e.g., exchanging of information in theform of data packets) of nodes 116, 118 in the cluster, and the nodes116, 118 can return results of the requested services to the hostdevices 108, 110. In one embodiment, the host devices 108, 110 canexchange information with the network modules 120, 122 residing in thenodes 116, 118 (e.g., network hosts) in the data storage systems 102,104.

In one embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. Volumes can span a portion of a disk, acollection of disks, or portions of disks, for example, and typicallydefine an overall logical arrangement of file storage on disk space inthe storage system. In one embodiment a volume can comprise stored dataas one or more files that reside in a hierarchical directory structurewithin the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the clustered network environment 100, the host devices 108, 110 canutilize the data storage systems 102, 104 to store and retrieve datafrom the volumes 132. In this embodiment, for example, the host device108 can send data packets to the network module 120 in the node 116within data storage system 102. The node 116 can forward the data to thedata storage device 128 using the data module 124, where the datastorage device 128 comprises volume 132A. In this way, in this example,the host device can access the volume 132A, to store and/or retrievedata, using the data storage system 102 connected by the networkconnection 112. Further, in this embodiment, the host device 110 canexchange data with the network module 122 in the host 118 within thedata storage system 104 (e.g., which may be remote from the data storagesystem 102). The host 118 can forward the data to the data storagedevice 130 using the data module 126, thereby accessing volume 1328associated with the data storage device 130.

It may be appreciated that implementing synchronous replication may beimplemented within the clustered network environment 100. In an example,a synchronous replication relationship may be established between thenode 116 (e.g., a first storage controller) and the node 118 (e.g., asecond storage controller). In this way, data operations, offloadedoperations, error handling operations, SAN control operations, and/orother operations and use cases (e.g., data access, control, andmetadata; offloaded and/or error handling operations on various storagecontainers such as files, SAN Logical Units, or Objects) may besynchronized between the data storage device 128 of node 116 and thedata storage device 130 of node 118 (e.g., synchronization at a file orLUN level of granularity). It may be appreciated that synchronousreplication may be implemented for and/or between any type of computingenvironment, and may be transferrable between physical devices (e.g.,node 116, node 118, etc.) and/or a cloud computing environment (e.g.,remote to the clustered network environment 100).

FIG. 2 is an illustrative example of a data storage system 200 (e.g.,102, 104 in FIG. 1), providing further detail of an embodiment ofcomponents that may implement one or more of the techniques and/orsystems described herein. The data storage system 200 comprises a node202 (e.g., host nodes 116, 118 in FIG. 1), and a data storage device 234(e.g., data storage devices 128, 130 in FIG. 1). The node 202 may be ageneral purpose computer, for example, or some other computing deviceparticularly configured to operate as a storage server. A host device205 (e.g., 108, 110 in FIG. 1) can be connected to the node 202 over anetwork 216, for example, to provide access to files and/or other datastored on the data storage device 234. In an example, the node 202comprises a storage controller that provides client devices, such as thehost device 205, with access to data stored within data storage device234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other media capable ofstoring data (e.g., optical and tape media), including, for example,data (D) and/or parity (P) information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 242. The data storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) and/or non-RAID optimization technique tooptimize a reconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202, such as a network storagecontroller, can respond to host device requests to manage data on thedata storage device 234 (e.g., or additional clustered devices) inaccordance with these host device requests. The operating system 208 canoften establish one or more file systems on the data storage system 200,where a file system can include software code and data structures thatimplement a persistent hierarchical namespace of files and directories,a non-persistent namespace, or a non-hierarchical namespace, forexample. As an example, when a new data storage device (not shown) isadded to a clustered network system, the operating system 208 isinformed where, in an existing directory tree, new files associated withthe new data storage device are to be stored. This is often referred toas “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and networkadapters 210, 212, 214 for storing related software application code anddata structures. The processors 204 and network adapters 210, 212, 214may, for example, include processing elements and/or logic circuitryconfigured to execute the software code and manipulate the datastructures. The operating system 208, portions of which are typicallyresident in the memory 206 and executed by the processing elements,functionally organizes the storage system by, among other things,invoking storage operations in support of a file service implemented bythe storage system. It will be apparent to those skilled in the art thatother processing and memory mechanisms, including various computerreadable media, may be used for storing and/or executing applicationinstructions pertaining to the techniques described herein. For example,the operating system can also utilize one or more control files (notshown) to aid in the provisioning of virtual machines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to ahost device 205 over a network 216, which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. The host device 205 (e.g., 108, 110 of FIG. 1) may be ageneral-purpose computer configured to execute applications. Asdescribed above, the host device 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the node 202 to access information requested by the hostdevice 205 (e.g., access data on a storage device managed by a networkstorage controller). The information may be stored on any type ofattached array of writeable media such as magnetic disk drives, flashmemory, and/or any other similar media adapted to store information. Inthe example data storage system 200, the information can be stored indata blocks on the disks 224, 226, 228 and/or within non-block storagedevices. The storage adapter 214 can include input/output (I/O)interface circuitry that couples to the disks over an I/O interconnectarrangement, such as a storage area network (SAN) protocol (e.g., SmallComputer System Interface (SCSI), iSCSI, hyperSCSI, Fibre ChannelProtocol (FCP)). The information is retrieved by the storage adapter 214and, if necessary, processed by the one or more processors 204 (or thestorage adapter 214 itself) prior to being forwarded over the system bus242 to the network adapter 210 (and/or the cluster access adapter 212 ifsending to another node in the cluster) where the information isformatted into a data packet and returned to the host device 205 overthe network 216 (and/or returned to another node attached to the clusterover the cluster fabric 215).

In one embodiment, storage of information on disk arrays 218, 220, 222can be implemented as one or more storage “volumes” 230, 232 that arecomprised of a cluster of disks 224, 226, 228 defining an overalllogical arrangement of disk space. The disks 224, 226, 228 that compriseone or more volumes are typically organized as one or more groups ofRAIDs. As an example, volume 230 comprises an aggregate of disk arrays218 and 220, which comprise the cluster of disks 224 and 226.

In one embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, whereas directories may be implemented asspecially formatted files in which information about other files anddirectories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume corresponds to at least a portion of physical storagedevices whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalstorage device locations, such as some available space from each of thedisks 224, 226, and/or 228. It will be appreciated that since a virtualvolume is not “tied” to any one particular storage device, a virtualvolume can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, Qtrees 235, objects, and files 240. Amongother things, these features, but more particularly LUNS, allow thedisparate memory locations within which data is stored to be identified,for example, and grouped as data storage unit. As such, the LUNs 238 maybe characterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In one embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumesstored on a data storage device, a target address on the data storagedevice can be used to identify one or more LUNs 238. Thus, for example,when the node 202 connects to a volume 230, 232 through the storageadapter 214, a connection between the node 202 and the one or more LUNs238 underlying the volume is created.

In one embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the one or more LUNs 238.

It may be appreciated that implementing synchronous replication may beimplemented for the data storage system 200. In an example, asynchronous replication relationship may be established between the node202 (e.g., a first storage controller) and another node (e.g., a secondstorage controller). In this way, data operations, offloaded operations,error handling operations, SAN control operations, and/or otheroperations and use cases (e.g., data access, control, and metadata;offloaded and/or error handling operations on various storage containerssuch as files, SAN Logical Units, or Objects) may be synchronizedbetween the node 202 and the other node (e.g., synchronization at a fileor LUN level of granularity). It may be appreciated that synchronousreplication may be implemented for and/or between any type of computingenvironment, and may be transferrable between physical devices (e.g.,node 202, host device 205, etc.) and/or a cloud computing environment(e.g., remote to the node 202 and/or the host device 205).

One embodiment of synchronous replication is illustrated by an exemplarymethod 300 of FIG. 3. A synchronous replication relationship may beestablished between a first storage controller hosting local storage anda second storage controller hosting remote storage. In an example, thefirst storage controller (e.g., hosted within a local network cluster)and the second storage controller (e.g., hosted within a remote networkcluster) may be configured according to a disaster recoveryrelationship, such that a surviving storage controller may provideclients with failover access to replicated data associated with a failedstorage controller (e.g., a switchover operation may be performed by thesurviving storage controller in order to obtain ownership of storagecomprising replicated data). The synchronous replication relationshipmay specify that operations directed to the first storage controller,such as data operations (e.g., a write operation), offloaded operations(e.g., a copy offload operation), error handling operations (e.g., anabort task, a task set, a LUN reset, a target reset, etc.), and/or SANcontrol operations (e.g., a modification to LUN metadata or otherstorage object metadata, such as a LUN size change or a LUN spacereservation), for commitment to the local storage are to besynchronously replicated to the second storage controller, such as forcommitment to the remote storage (e.g., commitment to both the localstorage and the remote storage for synchronization before an operationcomplete notification is provided back to a host that issued theoperation).

At 302, an operation for the local storage may be received. Theoperation may correspond to a storage area network (SAN) protocol. In anexample, the operation may be intercepted before the operation isdelivered to a file system (e.g., a network module may receive a hostrequest, comprising the operation, from a host, and an interceptor mayintercept the operation as the operation is being passed from thenetwork module to a data module for implementation). A configurationcache may be evaluated to determine whether a target object of theoperation is set for synchronous replication (e.g., the interceptor mayquery the configuration cache to determine whether a file, being writtento by the operation, is set for synchronous replication becausesynchronous replication may be set at a file level granularity or anyother level of granularity). At 304, the operation may be split tocreate a replication operation for the remote storage. For example, asplitter may split the operation responsive to the interceptordetermining that the target object is set for synchronous replication.In an example, the operation may be split based upon the operationcorresponding to a modification (e.g., a write operation, a change tometadata, etc.), which may improve efficiency by excluding the needlessreplication of read operations to the remote storage because suchoperations can be locally performed on the local storage.

At 306, responsive to the operation corresponding to a data operationand the replication operation corresponding to a replication dataoperation (e.g., the operation is a data operation such as a writeoperation), the data operation may be locally implemented upon the localstorage in parallel with the replication data operation being remotelyimplemented upon the remote storage. Because a relatively larger numberof data operations may be received and processed, data operations may beimplemented in parallel (e.g., passed to the first storage controllerfor local commitment to the local storage and sent to the second storagecontroller for remote commitment regardless of whether the local commithas finished), which may improve client response time because thereplication data operation may be sent to the second storage controllerfor commitment to the remote storage without first waiting for anacknowledgement that the data operation was successfully committed bythe first storage controller to the local storage.

At 308, responsive to the operation corresponding to an offloadoperation and the replication operation corresponding to a replicationoffloaded operation, the offloaded operation may be locally implementedupon the local storage in parallel with the replication offloadedoperation being remotely implemented upon the remote storage. In anexample, a copy engine that will service the offloaded operation may beautomatically selected based upon a replication relationship, such asthe synchronous replication relationship, and thus a consistent servicelevel may be provided where a time to complete the offloaded operationwill take a similar amount of time to complete regardless of a state ofthe replication relationship. That is, an offloaded operation of typecopy offload starts by selecting a copy engine based on a set ofcriteria. There is a hyper efficient copy engine called sis-clone whichuses sharing of blocks and avoids read and write load. For synchronousreplication this implementation makes a tradeoff where if thereplication relationship is in the process of coming back InSync, a lessefficient copy engine called ‘block copy engine’ is chosen, which addsreads and writes', and is a trade-off to prioritize establishing of asynchronous replication over efficiency of copy offload operation.

In an example, the offloaded operation may correspond to an operation,such as a copy offload operation, that is offloaded from an applicationserver to a storage server so that the application server can conserveresources from doing read/write host-based copy operations and/or otheroperations that could be implemented by the storage server. In anexample, the offloaded operation and/or the replication offloadedoperation may be serialized to deterministically control the order ofany overlapping inflight write operations. For example, an inflightwrite operation, overlapping a region targeted by the offloadedoperation, may be identified (e.g., an inflight log may be consulted toidentify a data operation as the inflight write operation). The inflightwrite operation may be queued until the offloaded operation and/or thereplication offloaded operation are complete. In an example, overlappinginflight operations and offloaded operations, such as replicationinflight operations, may be queued by the second storage controller,which may be beneficial for networks of higher latency. Responsive toreceiving a completion notification for the offloaded operation and aremote completion notification for the replication offloaded operation,an operation complete notification may be sent to a host that submittedthe operation.

At 310, responsive to the operation corresponding to an error handlingoperation and the replication operation corresponding to a replicationerror handling operation, the error handling operation may besynchronously implemented on the local storage. For example, the errorhandling operation may be implemented within a process flow that isdifferent than a process flow of a failed data operation, which mayreduce a likelihood that the error handling operation will also fail(e.g., an abort error handling operation may abort inflight writes, andthus is not processed as a regular data operation). The replicationerror handling operation may be performed as a best effortimplementation on the remote storage, which may be performed in parallelwith the implementation of the error handling operation. That is, thebest effort implementation may indicate that success of the operationdoes not rely upon success of the replication error handing operation.That is, the error handling operation does not wait for completion ofthe replication error handling operation and success of the errorhandling operation is independent of a completion status of thereplication error handling operation. For example, responsive toreceiving a completion notification for the error handling operation, anoperation complete notification may be sent to a host that submitted theerror handling operation notwithstanding a status of the replicationerror handling operation, such as regardless of whether the replicationerror handling operation has completed, failed, or is still pending. Inan example, the error handling operation may map to a set of dataoperations. The set of data operations may be grouped into an array thatis sent to the remote storage for implementation, which may reducenetwork bandwidth and/or improve efficiency because a reduced number ofmessages are sent across a network to the remote storage.

In an example, a reconciliation between the local storage and the remotestorage may be performed to address data divergence between the localstorage and the remote storage. That is, because of parallel splittingof the error handling operation, an operation could complete on thelocal storage and abort at the remote storage or the operation couldabort on the local storage and complete on the remote storage, thusresulting in divergence between the local storage and the remotestorage. In an example, the reconciliation may be performed in-line witha current data operation. In an example of performing thereconciliation, a set of hash tables may be used to track inflight dataoperations, such as data operations. Operations may be tagged withidentifiers associated with hash tables within the set of hash tables,such as where a data operation is tagged with an identifier of a hashtable. In this way, the data operation, such as a write operation thatwas to be aborted by the error handling operation, and/or a replicationof the data operation may be quickly identified by searching the hashtable, identified by the identifier used to tag the data operation, forinformation used to perform the reconciliation (e.g., informationregarding whether the data operation and/or the replication succeeded orfailed; a local region within the local storage and a remote regionwithin the remote storage that were targeted by the data operation andthe replication, which may be evaluated for data consistency within thelocal region and the remote region; etc.).

At 312, responsive to the operation corresponding to storage areanetwork (SAN) control operation (e.g., an operation used to modifystorage object metadata, such as metadata of a LUN) and the replicationoperation corresponding to a replication SAN control operation, the SANcontrol operation may be implemented upon the local storage. In anexample, the SAN control operation may be serially implemented with asecond SAN control operation based upon the SAN control operation andthe second SAN control operation targeting the same storage object(e.g., merely 1 SAN control operation may be implemented at any giventime for a particular LUN). Responsive to receiving a completionnotification for the SAN control operation, the replication SAN controloperation may be implemented upon the remote storage (e.g., thereplication SAN control operation may be refrained from being sent tothe second storage controller until the completion notification isreceived because SAN control operations may be sequentially processed).Responsive to receiving the completion notification for the SAN controloperation and a remote completion notification for the replication SANcontrol operation, an operation complete notification may be sent to ahost that submitted the operation. In this way, synchronous replicationmay be implemented for various types of operations.

FIGS. 4A-4C illustrate examples of a network storage environment forwhich synchronous replication may be implemented by a system 400. Afirst storage controller 406 (e.g., hosted within a first storagecluster located within a first building, city, or location) may beconfigured to provide a host 402, such as a client device, with accessto data stored within local storage 408, as illustrated in FIG. 4A. Thefirst storage controller 406 may be capable of communicating with asecond storage controller 412 (e.g., hosted within a second storagecluster located within a second building, city, or location) over anetwork 410.

The first storage controller 406 and the second storage controller 412may be configured as disaster recovery partners, such that a survivingstorage controller may perform, in response to identifying a failure ofthe other storage controller, a switchover operation (e.g., to obtainownership of storage devices owned by the failed storage controller) toprovide clients with failover access to replicated data in place of thefailed storage controller. In this way, client data access disruptionmay be reduced.

A synchronous replication relationship may be established between thefirst storage controller 406 and the second storage controller 412, suchas between the local storage 408 and the remote storage 414. Thesynchronous replication relationship may specify that data operations,offloaded operations, error handling operations, storage area network(SAN) control operations, and/or other types of operations for the localstorage 408 are to be implemented at both the local storage 408 andreplicated to the remote storage 414 (e.g., such as before a completionmessage is provided back to the host 402 for data operations, offloadedoperations, SAN control operations, etc., or where a best effort isimplemented for replication error handling operations). The synchronousreplication relationship may be specified at a relatively fine level ofgranularity, such as on a per file or LUN basis.

In an example, a data operation 404 may be received by the first storagecontroller 406, as illustrated in FIG. 4A. FIG. 4B illustrates the dataoperation 404 being implemented in parallel by the first storagecontroller 406 and the second storage controller 412. For example, thedata operation 404 may be locally implemented 422 by the first storagecontroller 406. The data operation 404 may be replicated 420 to thesecond storage controller 412 as a replication data operation that isremotely implemented 424 by the second storage controller 412. In anexample, the local implementation 422 of the data operation 404 and theremote implementation 424 of the replication data operation may beperformed in parallel (e.g., the replication data operation may be sentto the second storage controller 412 for remote implementation 424regardless of whether the local implementation 422 is complete or not).Once the local implementation 422 completes 430 and the remoteimplementation completes 432, a data operation complete notification 450may be sent to the host 402, as illustrated in FIG. 4C.

FIGS. 5A-5C illustrate examples of a network storage environment forwhich synchronous replication may be implemented by a system 500. Afirst storage controller 506 (e.g., hosted within a first storagecluster located within a first location) may be configured to provide ahost 502 with access to data stored within local storage 508, asillustrated in FIG. 5A. The first storage controller 506 may be capableof communicating with a second storage controller 512 (e.g., hostedwithin a second storage cluster located within a second location) over anetwork 510.

The first storage controller 506 and the second storage controller 512may be configured as disaster recovery partners, such that a survivingstorage controller may perform, in response to identifying a failure ofthe other storage controller, a switchover operation (e.g., to obtainownership of storage devices owned by the failed storage controller) toprovide clients with failover access to replicated data in place of thefailed storage controller. In this way, client data access disruptionmay be reduced.

A synchronous replication relationship may be established between thefirst storage controller 506 and the second storage controller 512, suchas between the local storage 508 and the remote storage 514. Thesynchronous replication relationship may specify that data operations,offloaded operations, error handling operations, storage area network(SAN) control operations, and/or other types of operations for the localstorage 508 are to be implemented at both the local storage 508 andreplicated to the remote storage 514. The synchronous replicationrelationship may be specified at a relatively fine level of granularity,such as on a per LUN basis.

In an example, an offloaded operation 504 may be received by the firststorage controller 506, as illustrated in FIG. 5A. For example, anapplication server may offload a copy operation as a copy offloadoperation to the first storage controller 506 (e.g., a storage server)for implementation upon the local storage 508. The offloaded operation504 may be split into a replication offloaded operation because theoffloaded operation 504 will result in a modification to data and/ormetadata and thus should be replicated to the remote storage 514 forconsistency. The offloaded operation 504 may be serialized with inflightoperations 516 being implemented by the first storage controller 506 forthe local storage 508, and the replication offloaded operation may beserialized with inflight replication operations being implemented by thesecond storage controller 512 for the remote storage 514. Accordingly,the inflight operations 516 may be queued as queued inflight operations516 a until the offloaded operation 504 is complete, as illustrated inFIG. 5B. In an example, the inflight replication operations 518 (e.g.,that overlap offloaded operations and/or replication offloadedoperations) may be secondarily queued as queued inflight replicationoperations 518 a until the replication offloaded operation is complete,which may be beneficial for networks of higher latency. In anotherexample, inflight operations 516 are queued by the first storagecontroller 506, but the inflight replication operations 518 are notqueued by the second storage controller 512.

The offloaded operation 504 may be locally implemented 520 by the firststorage controller 506 upon the local storage 508 in parallel withremote implementation 530 of the replication offloaded operation by thesecond storage controller 512 upon the remote storage 514. FIG. 5Cillustrates the first storage controller 506 generating a completionnotification 542 for the local implementation 520 of the offloadedoperation 504 upon the local storage 508. The second storage controller512 may generate a second completion notification 540 for the remoteimplementation 530 of the replicated offloaded operation upon the remotestorage 514. In an example, the offloaded operation is optimized at thesecond storage controller in the same manner as optimization occurs atfirst storage controller, such that efficiency is achieved in a similarmanner between the first and second storage controllers. The resultbeing highly efficient offloaded operations regardless of thereplication mechanism.

In this way, the remote storage 514 may mirror the local storage 508based upon the local implementation 520 of the offloaded operation 504upon the local storage 508 and the remote implementation 530 of thereplication offloaded operation upon the remote storage 514. Once theoffloaded operation 504 and the replication offloaded operationcomplete, an offloaded operation complete notification 546 may be sentto the host 502 (e.g., an application server that offloaded the copyoperation or a client that issued the copy operation). The queuedinflight operations 516 a and the queued inflight replication operations518 a may be dequeued for implementation as dequeued inflight operations516 b and dequeued inflight replication operations 518 b.

FIGS. 6A-6F illustrate examples of a network storage environment forwhich synchronous replication may be implemented by a system 600. Afirst storage controller 606 (e.g., hosted within a first storagecluster located within a first location) may be configured to provide ahost 602 with access to data stored within local storage 608, asillustrated in FIG. 6A. The first storage controller 606 may be capableof communicating with a second storage controller 612 (e.g., hostedwithin a second storage cluster located within a second location) over anetwork 610.

The first storage controller 606 and the second storage controller 612may be configured as disaster recovery partners, such that a survivingstorage controller may perform, in response to identifying a failure ofthe other storage controller, a switchover operation (e.g., to obtainownership of storage devices owned by the failed storage controller) toprovide clients with failover access to replicated data in place of thefailed storage controller. In this way, client data access disruptionmay be reduced.

A synchronous replication relationship may be established between thefirst storage controller 606 and the second storage controller 612, suchas between the local storage 608 and the remote storage 614. Thesynchronous replication relationship may specify that data operations,offloaded operations, error handling operations, storage area network(SAN) control operations, and/or other types of operations for the localstorage 608 are to be implemented at both the local storage 608 andreplicated to the remote storage 614. The synchronous replicationrelationship may be specified at a relatively fine level of granularity,such as on a per file or LUN basis.

In an example, a storage area network (SAN) control operation 604 may bereceived by the first storage controller 606, as illustrated in FIG. 6A.The SAN control operation 604 may be split into a replication SANcontrol operation because the SAN control operation 604 will result in amodification to storage object metadata, such as LUN metadata, and thusshould be replicated to the remote storage 614 for consistency. The SANcontrol operation 604 may be locally implemented 630 in a serial mannerwith other inflight SAN control operations 616 that target the samestorage object, such as the same LUN. In this way, no more than one SANcontrol operation may be implemented for a LUN at any given time, asillustrated in FIG. 6B. FIG. 6C illustrates the first storage controller606 generating a completion notification 640 for the localimplementation 630 of the SAN control operation 604 upon the localstorage 608.

Responsive to receiving the completion notification 640 for the localimplementation 630 of the SAN control operation 604, the replication SANcontrol operation may be remotely implemented 650 in a serial mannerwith other inflight replication SAN control operations 618 that targetthe same storage object, as illustrated in FIG. 6D. For example, thereplication SAN control operation may not be implemented and/or sent tothe second storage controller 612 until the SAN control operation 604completes. The second storage controller 612 may generate a secondcompletion notification 660 for the remote implementation 650 of thereplication SAN control operation upon the remote storage 614, asillustrated in FIG. 6E. In this way, the remote storage 614 may mirrorthe local storage 608 based upon the local implementation 630 of the SANcontrol operation 604 upon the local storage 608 and the remoteimplementation 650 of the replication SAN control operation upon theremote storage 614. Once the SAN control operation 604 and thereplication SAN control operation complete, an SAN control operationcomplete notification 670 may be sent to the host 602, as illustrated inFIG. 6F.

FIGS. 7A-7D illustrate examples of a network storage environment forwhich synchronous replication may be implemented by a system 700. Afirst storage controller 706 (e.g., hosted within a first storagecluster located within a first location) may be configured to provide ahost 702 with access to data stored within local storage 708, asillustrated in FIG. 7A. The first storage controller 706 may be capableof communicating with a second storage controller 712 (e.g., hostedwithin a second storage cluster located within a second location) over anetwork 710.

The first storage controller 706 and the second storage controller 712may be configured as disaster recovery partners, such that a survivingstorage controller may perform, in response to identifying a failure ofthe other storage controller, a switchover operation (e.g., to obtainownership of storage devices owned by the failed storage controller) toprovide clients with failover access to replicated data in place of thefailed storage controller. In this way, client data access disruptionmay be reduced.

A synchronous replication relationship may be established between thefirst storage controller 706 and the second storage controller 712, suchas between the local storage 708 and the remote storage 714. Thesynchronous replication relationship may specify that data operations,offloaded operations, error handling operations, storage area network(SAN) control operations, and/or other types of operations for the localstorage 708 are to be implemented at both the local storage 708 andreplicated to the remote storage 714. The synchronous replicationrelationship may be specified at a relatively fine level of granularity,such as on a per file or LUN basis.

In an example, an error handling operation 704 may be received by thefirst storage controller 706, as illustrated in FIG. 7A. The errorhandling operation 704 may be split into a replication error handlingoperation because the error handling operation 704 will result in amodification to data and/or metadata (e.g., an abort of data operationsthat would otherwise write data to the local storage 708) and thusshould be replicated to the remote storage 714 for consistency. Theerror handling operation 704 may be locally implemented 720 by the firststorage controller 706 upon the local storage 708 in a synchronousmanner such that the error handling operation 704 may be performedwithin a different process, such as a different thread, than inflightoperations 716 that may have led to the error handling operation 704(e.g., failed data operations), which may mitigate a likelihood that theerror handling operation 704 also fails, as illustrated in FIG. 7B.Replicating the error handling operation can reduce processing time atthe second storage controller. That is, since the first storagecontroller is waiting for the second storage controller to finish, theerroring handling operation is replicated to cancel processing by thesecond storage controller so that the first storage controller is notheld up waiting on the second storage controller to fully process anoriginal operation or message.

The replication error handling operation may be remotely implemented730, such as in parallel with the local implementation 720 of the errorhandling operation 704 and synchronously with inflight replicationoperations 718 (e.g., implemented within a different process), by thesecond storage controller 712 upon the remote storage 714 as a besteffort implementation. The best effort implementation may specify thatsuccess of the error handling operation 704 does not rely upon successof the replication error handling operation. For example, in response tofirst storage controller 706 generating a complete notification 742 forthe local implementation 720 of the error handling operation 704, anerror handling operation success notification 746 may be sent to thehost 702 regardless of whether the best effort of the remoteimplementation 730 of the replication error handling operationsuccessfully completed, as illustrated in FIG. 7C.

FIG. 7D illustrates an example of performing a reconciliation 762between the local storage 708 and the remote storage 714 because thereplication error handling operation was implemented as a best effort.That is, because of parallel splitting of the error handling operation704, an operation could complete on the local storage 708 and abort atthe remote storage 714 or the operation could abort on the local storage708 and complete on the remote storage 714, thus resulting in divergencebetween the local storage 708 and the remote storage 714. Accordingly,the reconciliation 762 may be performed to determine whether there isthe divergence (e.g., if the data operation aborted at the local storage708 and completed at the remote storage 714, then the reconciliation 762may modify the remote storage 714 into a state corresponding to thelocal storage 708 where the data operation was aborted or may modify thelocal storage 708 into a state corresponding to the remote storage 714where the data operation was completed). In an example, thereconciliation 762 may be performed in-line with a current dataoperation 760 (e.g., a read or write to a region affected by the dataoperation that may or may not have been aborted by the replication errorhandling operation).

Still another embodiment involves a computer-readable medium comprisingprocessor-executable instructions configured to implement one or more ofthe techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 8, wherein the implementation 800comprises a computer-readable medium 808, such as a CD-ft DVD-R, flashdrive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 806. This computer-readable data 806, such asbinary data comprising at least one of a zero or a one, in turncomprises a processor-executable computer instructions 804 configured tooperate according to one or more of the principles set forth herein. Insome embodiments, the processor-executable computer instructions 804 areconfigured to perform a method 802, such as at least some of theexemplary method 300 of FIG. 3, for example. In some embodiments, theprocessor-executable computer instructions 804 are configured toimplement a system, such as at least some of the exemplary system 400 ofFIGS. 4A-4C, at least some of the exemplary system 500 of FIGS. 5A-5C,at least some of the exemplary system 600 of FIGS. 6A-6F, and/or atleast some of the exemplary system 700 of FIGS. 7A-7D, for example. Manysuch computer-readable media are contemplated to operate in accordancewith the techniques presented herein.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), EEPROM and/or flash memory, CD-ROMs, CD-Rs, CD-RWs, DVDs,cassettes, magnetic tape, magnetic disk storage, optical or non-opticaldata storage devices and/or any other medium which can be used to storedata.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: evaluating operations targeting first storage to identify data operations and metadata operations; executing the metadata operations upon the first storage in parallel with executing the data operations based upon the metadata operations being non-overlapping with respect to pending operations; executing and replicating the data operations upon the first storage and second storage in parallel; and storing an operation into a queue based upon the operation depending upon prior execution of a pending operation.
 2. The method of claim 1, comprising: completing the pending operations while the operation is within the queue.
 3. The method of claim 2, comprising: de-queuing and executing the operation based upon execution of the pending operations completing.
 4. The method of claim 1, comprising: storing the operation into the queue based upon the operation overlapping a region targeted by the pending operation.
 5. The method of claim 1, comprising: replicating the operations to create replicated operations to execute upon the second storage.
 6. The method of claim 5, comprising: serially executing non-overlapping metadata operations and overlapping metadata operations upon the first storage before executing corresponding replicated operations upon the second storage.
 7. The method of claim 6, comprising: executing queued operations within the queue upon completion of the pending operations.
 8. The method of claim 6, comprising: executing replicated metadata operations upon completion of the pending operations.
 9. The method of claim 1, comprising: identifying operations as non-overlapping operations based upon the operations targeting non-overlapping regions with respect to the pending operations.
 10. The method of claim 1, comprising: identifying operations as overlapping metadata operations based upon the operations depending upon prior execution of the pending operations.
 11. The method of claim 1, comprising: maintaining the queue within which operations overlapping pending operations are to be stored.
 12. A non-transitory machine readable medium comprising instructions for performing a method, which when executed by a machine, causes the machine to: evaluate operations targeting first storage to identify data operations and metadata operations; execute the metadata operations upon the first storage in parallel with executing the data operations based upon the metadata operations being non-overlapping with respect to pending operations; execute and replicating the data operations upon the first storage and second storage in parallel; and store an operation into a queue based upon the operation depending upon prior execution of a pending operation.
 13. The non-transitory machine readable medium of claim 12, wherein the instructions cause the machine to: complete the pending operations while the operation is within the queue.
 14. The non-transitory machine readable medium of claim 13, wherein the instructions cause the machine to: de-queue and execute the operation based upon execution of the pending operations completing.
 15. The non-transitory machine readable medium of claim 12, wherein the instructions cause the machine to: store the operation into the queue based upon the operation overlapping a region targeted by a pending operation.
 16. The non-transitory machine readable medium of claim 12, wherein the instructions cause the machine to: replicate the operations to create replicated operations to execute upon the second storage.
 17. The non-transitory machine readable medium of claim 16, wherein the instructions cause the machine to: serially execute non-overlapping metadata operations and overlapping metadata operations upon the first storage before executing corresponding replicated operations upon the second storage.
 18. The non-transitory machine readable medium of claim 16, wherein the instructions cause the machine to: execute queued operations within the queue upon completion of the pending operations.
 19. The non-transitory machine readable medium of claim 16, wherein the instructions cause the machine to: execute replicated metadata operations upon completion of the pending operations.
 20. A computing device comprising: a memory comprising machine executable code; and a processor coupled to the memory, the processor configured to execute the machine executable code to cause the processor to: evaluate operations targeting first storage to identify data operations and metadata operations; execute the metadata operations upon the first storage in parallel with executing the data operations based upon the metadata operations being non-overlapping with respect to pending operations; execute and replicating the data operations upon the first storage and second storage in parallel; and store an operation into a queue based upon the operation depending upon prior execution of a pending operation. 